Heretofore, as the material for raceway member (fixed member and moving member having a rolling raceway surface) for a rolling support device, SUJ2 has been used for bearing steel and steel materials corresponding to SCR420 and SCM420 have been used for case hardening steels. Since the rolling support device is used generally under repetitive shearing stress at a high surface pressure, for ensuring rolling contact fatigue life endurable to the shearing stress, hardness is adjusted to HRC 58 to 64 by applying quenching and tempering for case the bearing steel and applying quenching and tempering after carburizing or carbonitriding for case hardening steels.
However, the working circumstances for the rolling support devices are versatile. For example, in a case of a rolling support device for machineries used under a corrosive circumstance such as liquid crystal or semiconductor production facilities or foodstuff machines, when a bearing steel is used as the material, it may sometimes suffer from rust in an early stage to reach the bearing life. Thus, stainless steels are often used as the material when such corrosion resistance is required.
Stainless steels are generally classified into austenitic series, ferritic series, austenite-ferrite two phase series, martensitic series and precipitation hardened series. In the rolling bearing, since the contact portion between a rolling element and an outer ring or an inner ring undergoes wear and large shearing stress, martensitic stainless steels having high hardness and excellent in wear resistance are used mainly. Among them, SUS 440C having the highest hardness has been used most frequently. However, the martensitic stainless steel represented by SUS 440C is poor in the corrosion resistance compared with other stainless steels and is not always satisfactory.
On the other hand, those stainless steels other than the martensitic steels such as austenitic or ferritic steels are excellent in the corrosion resistance but have no sufficient hardness corresponding to the requirement in the rolling support device, so that no sufficient wear resistance and rolling life can be obtained. Particularly, in a case of requiring the corrosion resistance, those applied with hard Cr plating or coating layer comprising a fluorine-containing material to the carburized or carbonitrided case hardening steel or those applied with various kinds of other corrosion resistant layers than described above have been used. However, the deposited layer not in contiguous with the matrix phase involves a problem that it lacks in the layer strength, tending to cause peeling and no sufficient durability can be obtained for the rolling support device.
The present invention has been developed in order to solve the various problems that conflict to each other in the prior art and it is a first subject thereof to provide a rolling support device excellent in both of the characteristics of the corrosion resistance and the durability.
On the other hand, in the apparatus where magnetic fields cause a problem such as in production facilities for liquid crystal or semiconductor devices, medical inspection apparatus or linear motor cars, when a driving section is formed of a magnetic material, surrounding magnetic fields are disturbed upon driving to sometimes deteriorate the performance of the apparatus. Accordingly, in constituent components for the rolling support device used in such apparatus, those made of non-magnetic materials have to be used. Heretofore, constituent components made of beryllium-copper alloys or ceramics have been used.
However, the beryllium-copper alloys tend to suffer from oxidation and since the oxides are toxic substance, use of the beryllium-copper alloys as the material for the constituent components in the rolling support device is not preferred with a view point of environmental problems. Further, those made of beryllium-copper alloys have a low hardness of about 40 as Rockwell C hardness (HRC), so that they have a problem also in view of durability. Further, when ceramics are used as the material for constituent components in the rolling support device, they result in problems of increasing the cost and providing difficulty in enlarging the size and reducing the thickness.
Accordingly, precipitation hardening type austenitic non-magnetic steels such as Mn—Cr—V series or Mn—Cr—Ni—V series have been used in recent years. However, although such steels are somewhat excellent in the corrosion resistance over the martensitic stainless steels but still not yet sufficient. In addition, since the hardness is about 45 (HRC), such steels can not solve the problem of the durability when used as they are.
The method of improving the surface hardness of the steels described above can include, at first, a method of forming a hard ceramic coating on the surface by a PVD method or CVD method. In this method, since the ceramic layer is formed not in contiguous with the base metal, the layer may possibly be peeled from the base metal upon undergoing high contact stress. Accordingly, this method can not provide a sufficient durability as the constituent components for the rolling support device.
There can be mentioned a second method of work hardening the surface by cold working. This method involves a problem of giving magnetic property since fabrication induced transformation is caused to make the austenite into martensite.
There can be mentioned, as a third method, a heat treatment such as carburizing or carbonitriding. However, the austenitic non-magnetic steels are less carburized, different from general bearing steels. In addition, since increase of the hardness utilizing the martensitic transformation can not be expected in the steels, it is necessary to harden the surface layer, for example, by precipitating a great amount of carbides or carbonitrides. In this case, since Cr having high affinity with carbon is precipitated predominantly as carbides to possibly lower the non-magnetic property or the corrosion resistance.
As described above, no constituent components for the rolling support device comprising a non-magnetic material and having sufficient durability and corrosion resistance have yet been obtained by the prior art method. A second subject of the present invention is to provide a rolling support device comprising constituent components which are non-magnetic and excellent in the durability and the corrosion resistance.